The invention generally relates to thyristors which include a semiconductor body having an anode-side base zone of a first conductance type and having a cathode-side base zone of the second, opposite conductance type, with cathode-side and anode-side emitter zones, and to a method for producing such thyristors.
Despite the high power levels which thyristors can handle, they are sensitive, especially when they are connected deliberately or in an unmonitored manner to high voltage. The breakdown triggering which occurs then can lead to destruction of the thyristor. Light-triggerable thyristors are particularly at risk, since the triggering power that is supplied is very low in this case and, in some circumstances, is not sufficient to switch on the thyristor correctly. Improved light-Triggerable high-power thyristors for voltages of up to 8 kV are described by H.-J, Schulze, M. Ruff, B. Baur, H. Kabza, F. Pfirsch, U. Kellner in xe2x80x9cLight-triggered 8 kV Thyristors with a New Type of Integrated Breakover Diodexe2x80x9d in the Proceedings of the xe2x80x9cInternational Symposium for Semiconductor Power Devicesxe2x80x9d, May (1996).
DE 196 50 762 specifies an improved light-triggerable high-power thyristor with a predetermined carrier life profile and proposes a method for producing such a thyristor, by means of which the breakdown triggering of the thyristor in the thyristor operating temperature range is made largely independent of the temperature. To this end, in a thyristor composed of a semiconductor with an anode-side base zone of a first conductance type and a cathode-side base zone of a second conductance type, with anode-side and cathode-side emitter zones, with a region in the cathode-side base zone which, by virtue of its geometry, has a breakdown voltage which is less than that in the other regions in the cathode-side base zone and in the edge of the semiconductor body, a defect zone in which the life of the free charge carriers is reduced is provided on the anode side underneath the region where the breakdown voltage is reduced. This measure governs the breakover voltage of the thyristor in the forward direction. The position of the minimum in the carrier life profile is used to determine whether the space charge zone, which propagates from the cathode side, does or does not overlap the zone of reduced carrier life when the forward voltages are sufficiently high. An additional generation current is produced if the zones overlap.
However, the thyristors according to the above prior art cannot be loaded again with a surge voltage until after a specific recovery time. Should a voltage surge occur before this time has elapsed, however, then there is a risk of the thyristor being destroyed by the current filamentation that occurs in the cathode surface.
An object of the present invention is to provide a thyristor with integrated recovery time protection, which may be loaded with a voltage surface once again even within the recovery time without in the process being destroyed by current filamentation occurring in the cathode surface, and to specify a method for producing such a thyristor.
The object is preferably achieved by a thyristor having the features of claim 1, and by a method for producing such a thyristor having the steps in claim 4. Preferred embodiments of the invention are the subject matter of the dependent claims.
The integrated voltage surge protection is achieved, according to the invention, by raising the concentration of free charge carriers in the central region of the component when the thyristor is connected in the blocking direction. The blocking current is thus increased when a blocking voltage load is applied to the thyristor. The increased concentration of free charge carriers is produced by particle irradiation of a zone in the anode-side base of the thyristor. This results in lattice faults in the crystal, which act as recombination and generation centers for charge carriers. This defect zone with a reduced carrier life is in this case arranged in the anode-side base such that, when the thyristor is connected in the blocking direction, it overlaps the space charge zone propagating from the anode side, and the minimum carrier life in the component occurs underneath the emitter. In the forward direction (in the blocking region) of the thyristor, the defect zone with the reduced carrier life is, in contrast, located inside the neutral anode-side base. This means that the blocking current in the forward direction (leakage current) is not increased. The defect zone extends over an area in the thyristor which depends on the desired reduction in the carrier life in the defect zone.
The thyristor according to the invention, which includes a semiconductor body having an anode-side base zone of a first conductance type and having a cathode-side base zone of the second, opposite conductance type, having cathode-side and having anode-side emitter zones, where a defect zone is arranged within the anode-side base zone on the anode side, in which the free charge carriers have a reduced life, with a predetermined thickness of at least 20 xcexcm.
The defect zone preferably essentially has defects in the crystal lattice, which are produced by irradiation with high-energy particles. In general, the thickness of the defect zone can be selected as a function of the generation current, such that the desired generation current is produced.
In order to produce a thyristor according to the invention, the semiconductor is irradiated such that this results in a region with reduced charge carrier life within the base of the thyristor. The production method for a thyristor is characterized in that, in order to produce the defect zone, anode-side irradiation of predetermined regions of the semiconductor body with charged particles is carried out, followed by heat-treatment of the semiconductor body in order to stabilize the defect zone.
Protons or xcex1-particles are preferably used for irradiation of the predetermined regions. A dose of approximately 5xc2x7109 to 1012 cmxe2x88x922 for xcex1-particles and from 1011 to 1013 cmxe2x88x922 for protons is selected for irradiation of the predetermined regions.